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Mana worked for Dogen Takayanagi and was assigned to be Shin Natsume's girlfriend. She was ordered to observe and collect data about him for the Takayanagi family. She helped Shin create the Team KATANA, to get even more data and make it less boring for Shin. Over time she began to truly love him, however she realized that he views his sister Maya Natsume more like a lover than a sibling.

While she does truly love Shin, she still carries out the orders as intended. She watches Shin very closely as she keeps 3 GPS trackers on Shin at all times and assigns her bodyguard Emi Isuzu to videotape him periodically. She uses her acupuncture skills as a member of the Medical club to save the lives of most of Shin's opponents. As Dogen had plans to force Mitsuomi Takayanagi into fighting Shin, Mana plays her role by starting an affair with Mitsuomi and actively spreads it around. Although she doesn't actually have feelings for Mitsuomi, she does have respect for him as he is like herself. She does have a lot of faith in Mitsuomi, she believes he is the only one capable of stopping Shin when he loses control of himself.

Bunshichi Tawara doesn't seem to like her very much, when he finds out she one of the conspirators to Dogen's plan. Maya also doesn't seem to like her, the feeling mutual, since Maya will always be number one to Shin.

As Mitsuomi enters Toudou academy, he is taken under Shin's wing. After Shin nearly kills someone for fighting Maya, Mitsuomi realizes the man is dying. Mana arrives and uses her acupuncture to save the man's life. Afterward she immediately asks Mitsuomi if he can meet her alone. When Mitsuomi goes to meet her she forces herself on him. During the act she reveals that Maya and Shin are more like lovers than siblings, and that Shin has nearly killed almost every opponent he's ever fought.

Later as Mitsuomi talks to Bunshichi, he reveals he knows of the affair. When Mitsuomi asks how, he says Mana has been spreading it around. One night after having sex, Mitsuomi asks why Mana is so sexy. Her answer was to provide him a gift that has the answer in it. When Mitsuomi opens it, it contains ear rings and a memory stick for a camcorder. He asks Bunshichi to watch the video with him. Initially the video is of Shin and Mana's early relationship, some surveillance footage, but suddenly shifts dramatically to Shin killing innocents for a distraction. Mitsuomi is overwhelmed by fear and Bunshichi is upset about his friend's behavior.

After Shin severely beats and nearly kills the majority of his gang, since they planned to punish Maya for being the "KATANA Hunter" that was taking out members of the gang. Bunshichi heads out to beat sense into Shin. He notices Emi, who was video taping him with a hidden camera. Through this encounter, he gains possession of a tracking device and uses it to find Shin. Shin and Mana are meeting with Dogen. Mana reveals she keeps 3 tracking devices on Shin at all times. Bunshichi doesn't care and immediately tells her to shut up, and calls her ugly, which Dogen finds hilarious. Mana yells at Fu Chi'en for allowing Bunshichi to get to them, but Fu Chi'en shrugs it off and says that Shin and Bunshichi were fated to fight anyway. Bunshichi challenges Shin to a fight, despite the fact Shin has the Reiki it doesn't go well for him. After Shin stabs Bunshichi in the legs for quite a while Mana can't take it any more and yells at him, stopping him. She then demands he give her Reiki, which he hesitantly does.

The second Reiki leaves Shin's hand Bunshichi resumes his attack and beats up Shin. Mana doesn't want to give Reiki back to Shin even though Dogen says he will lose without. After Bunshichi beats Shin down, he tries to crawl for the Reiki. Mana pulls it back, and Bunshichi knocks Shin out. It was later revealed by Fu Chi'en that Shin could easily beat Bunshichi even without Reiki but he hesitates because he didn't want to kill his best friend and the surrounding people.

Afterward when Shin is in the hospital Mana visits him every day. When she tries to feed him and he resists she has some of the Takayanagi family's men hold his mouth open. When he spits it out, the men beat him up. She reveals Bunshichi has been released from the hospital, and the 24 hour observation on Shin has been canceled. She reveals her duty as an assigned girlfriend is over, and while she hated the order initially she has grown to love him. She kisses him and tells him she will return tomorrow as a friend.

Mana later invites Maya to meet her outside. She attempts to throw one of her acupuncture needles at her, but Maya catches it. She tells Maya how they created the gang Katana, to make it more interesting for Shin as he was being observed. He almost seemed like a normal high school student for a while. Just as Shin started to see the light of friendship, Maya came and ruined it all with her "Katana Hunting". Maya insists her brother was in the dark because he wanted to be, but he was lucky to have two great women looking after him. Mana later tells Mitsuomi, Maya utterly defeated her.

As the schools annual election tournament arrives, Mana helps to treat the injured. As she goes to treat Maya's wrist, she claims she could make her whole right arm useless for the rest of her life. Instead she simply heals her, but says if she ever gets the chance to win against her she will take it in an instant. Soon after Kagesada Sugano informs the other members Shin is meeting with Dogen, Mana leaves to investigate what is going on. She is captured by Fu Chi'en, along with Emi, and are tied up and gagged in order to prevent their interference. Fu Chi'en is under orders to activate Shin's power by attacking Maya. The plan to setting Shin off works. During the fight, Emi cuts the ropes binding her and Mana, and attacks Fu Chi'en. Mana runs to get Mitsuomi, believing only he could stop Shin in that state. In the end it leads to Shin blasting Mitsuomi with a large quantity of ki. Mitsuomi was taken to the hospital but he was released. Later that night, he is returned to the hospital after coughing up blood.

As the finals arrive, Mitsuomi defeats the Joint Team in the finals all by himself. As he leaves the arena, he grabs his chest and meets Mana in the hall, he collapses on her and vomits blood behind her. She then explains that the large quantity of ki fired into his heart has sped it up, far beyond anything drugs could mimic. As a result his body is becoming super oxygenated, vitalizing his muscles, improving his metabolism, and even improving his brain functions. So three minutes, he gets super human abilities. If he fights longer than that his heart rate will surpass 200 beats per minute, and will rupture. Even if Mitsuomi doesn't fight he has 2-3 years of life left.

When Shin challenges Mitsuomi to a fight to determine the executive council's president, Mana observes the fight and prevents Maya's interference. She points out Shin is fighting without the assistance of his Dragon's Eye. Mana says this is because he isn't fighting Mitsuomi, he's fighting against his own power, and his fate. However, when Mitsuomi beats Shin down Mana jumps in the way and stops the fight herself. During this time Shin's will lost to his powers, and in his insane state he uses the Takayanagi family's secret technique, the Forged Iron Needle Attack to blast through Mana and into Mitsuomi. He subsequently attacks everyone in the room. When he regains himself, he goes over to the dying Mana. Mana tells the now crying Shin that she always knew this day would come, from the day she fell in love with him. As her parting words to Maya, she warned not to let Mitsuomi walk the same road as Shin. With the last of her energy, she assisted Shin in taking his own life.

As a member of the Medical club and comes from a family of doctors. Mana is very skilled in acupuncture techniques. She is capable of treating many types of injuries ranging from severe physical injuries to Mitsuomi's heart condition.

She uses relatively large needles in her acupuncture and knows where there are points to disable movement, and paralyze appendages permanently. She can also throw her needles much like a Bo-Shuriken if she needs to attack someone.